The presently available digital broadcast includes a communications satellite (CS) broadcast, cable broadcast, Internet broadcast, and the like. These digital broadcasts are received by a set-top box (STB), for example. An STB, which is connected to a television, has a function of receiving and converting video signals and an interface for connecting a telephone line and a personal computer.
FIG. 5 is a schematic diagram of a transmitting unit 10 and a receiving terminal 20 for digital broadcast. The transmitting unit 10 transmits multiplex data (MPEG2-TS), in which video and audio data, computer program, EPG (electronic program guide) data are combined, to the receiving terminal 20. The transmitting unit 10 includes a video server 14 for compressing video and audio data and an application server 12, or a general purpose computer. The receiving terminal 20 includes an STB 22 for receiving a digital data broadcast and a television 24 having a visual output unit and audio output unit. The STB 22 may be built into the television 24.
As shown in FIG. 6(a), the video server 14 comprises MPEG 2 (Motion Picture Expert Group phase 2) encoders 30 which compress video and audio data 1, 2, 3, and 4 including audio data (audio 1, 2, 3, and 4) and video data (video 1, 2, 3, 4) in accordance with the MPEG2 standard; a multiplexer 32 which multiplexes the compressed video and audio data 1, 2, 3 and 4, EPG and the like; and a transmitter 34 for transmitting the multiplexed data (MPEG2-TS). FIG. 6(b) shows an overview of the data (MPEG2-TS) transmitted by the transmitting unit 10. In FIG. 6(b), a plurality of MPEG 2 data are included in the same frequency band in a time-division manner.
As shown in FIG. 7, the STB 22 comprises a receiver 40 for receiving the data (MPEG2-TS) transmitted from the transmitting unit 10; a demultiplexer 42 for separating the multiplexed data (MPEG2-TS); an MPEG2 decoder 44 for decoding the video and audio data compressed in the MPEG2 standard; a video decoder 46 for converting the decoded video data into a video signal for television display; an input device 52 for operating the STB 22; a communication device 48 for communicating the transmitting unit 10 via communication lines such as telephone lines; and a microprocessor unit (MPU) 50 for controlling these devices included in the STB 22.
In the case of CS broadcasting, the receiver 40 receives digital broadcast using a parabolic antenna. The received data (MPEG 2-TS), which is the multiplexed data, is separated into video and audio data by the demultiplexer 42. The video and audio data are transmitted to the MPEG2 decoder 44, and the EPG data is transmitted to the MPU 50. The video and audio data are decoded in the decoder 44. The volume of the decoded audio data is adjusted in an amplifier (not shown), and then sent to a speaker integrated in the television 24, for example. The decoded video data is converted into video signals for television display, and then sent to the television 24.
The EPG data transmitted to the MPU 50 is stored in a memory (not shown). The input device 52 is used for selecting a program to watch, changing the display of the EPG, and so on. For example, when an operation button of the input device 52 is pushed, the MPU receives the information that the button has been pushed. For example, when a program to watch is selected, the MPU 50 changes the MPEG2 data transmitted from the demultiplexer 42 to the MPEG2 encoder 44 to the program data selected in the above step. For example, when display control of the EPG data is performed in the input device 52, the MPU 50 transmits the EPG data to the video encoder 46. In the encoder 46, the EPG data is converted into video signals for television display, and then it is displayed on the screen of the television 24. The MPU 50 transmits watched program information to the transmitting unit 10 via the communication device 48. The application server 12 receives the watched program information and then calculates a viewing fee on the basis of the watched program information.
In these days, STBs having the function of not only receiving digital broadcast, but also browsing the Web on the Internet are becoming increasingly common. FIG. 8 is an overview of the connection between the Internet 16 and a receiving terminal 20 and a transmitting unit 10 in a digital broadcast system. Web data is transmitted from the Internet 16 to the receiving terminal 20 via the transmitting unit 10. The term “web data” used herein includes web page data such as HTML (Hyper Text Markup Language) file, image file, audio file and the like. The image file includes still picture and motion picture.
FIG. 9(a) shows an example of a web page 60. The web page 60 includes a picture 62, characters 64, and links 70, 72, and 74. The links 70, 72, and 74 are linked to other web pages. As shown in FIG. 9(b), links are provided to diagonally shaded areas 82, 84, and 86. Selecting one of the links 70, 72, and 74 by clicking on it, the user can browse a web page linked to the selected link.
As shown in FIG. 10(a), the web data transmitted from the Internet 16 to the application server 12 is sent to the multiplexer 32 in the video server 14. The web data, EPG data, MPEG2 data, and the like are then multiplexed and sent to the STB 22. An example of the transmitted data (MPEG2-TS) included in the same frequency band in a time-division manner is shown in FIG. 10(b).
As shown in FIG. 11, the STB 22 receives the web data (MPEG2-TS) transmitted from the transmitting unit 10. The received data is separated in the demultiplexer 42, and then transmitted to the MPU 50. The MPU 50 activates a web browser (a software for browsing the Web), and transmits graphic output of a web page to the television 24 via the video encoder 46. An image 80 shown in FIG. 12(a), which is displayed by the web browser, is converted into video signals, and then sent to the television 24. The volume of audio data is adjusted in an amplifier (not shown), and then sent to the television 24.
The input device 52 can be used for selecting one of the links by positioning a cursor 76 shown in FIG. 12(b) in the link and clicking a mouse button, for example. The function of selecting a link using a cursor is provided to the web browser, and the selection of a link is executed by the MPU 50. The MPU 50 sends selected link information to the transmitting unit 10 via the communication device 48. The application server 12 receives the selected link information from the receiving terminal 20, and requests the Internet 16 to transfer a web page linked to this link. When the requested web page is transferred from the Internet 16 to the application server 12, the server 12 sends the web page to the receiving terminal 20 in the same manner as described above.
As stated above, it is possible to browse the Web using an STB. However, as compared to the case where digital broadcast is received, a higher-speed MPU and a larger-capacity memory must be used when the web browser is used. In addition, since there is little compatibility between the MPUs and between the operating systems (OS) used in various STBs, the web browsers may often vary among the STBs. Even if the same web browsers are used in the STBs, functions may vary among STBs due to the addition of function enhancement software such as plug-in software. Thus, the variations between the web browsers may cause a failure of displaying a web page on the screen.